Snecma Tests Scale Model of Open-rotor Engine

Snecma is preparing a high-speed test to demonstrate the open rotor’s fuel-burn advantage.

Snecma plans soon to start another phase of open-rotor engine testing using a one-fifth scale model, in a research and technology effort that epitomizes how laborious developing a new commercial engine concept can be. The concept, based on contra-rotating high-speed propellers, may not find itself in service before 2025. Nevertheless, trials aimed at cutting noise while retaining the huge efficiency advantage of the open rotor’s architecture are well under way.

Snecma plans more evaluations this month and next at the Onera S1 wind tunnel in Modane, France. “This time it will be a high-speed test, since we want to demonstrate the engine’s potential for reducing fuel consumption,” propeller module manager Marc Doussinault explained. The company aims to beat the fuel burn of the current CFM56 by 25 to 30 percent.

The previous series of tests, which lasted two weeks in July, focused on the engine’s low-speed aerodynamics and acoustics. The French engine maker’s engineers studied several propeller pairs. They used the Hera testbed, aimed at maturing the design of the propellers. In two series of tests, one used the baseline propeller pair, which had already undergone testing, and the other a new configuration. The latter arrangement allows the propellers to rotate at different speeds, “giving the engine greater operating freedom and enhancing both aeroacoustic and aerodynamic performance,” according to Snecma.

Test results validated design software programs. Moreover, they helped engineers understand the physical phenomena involved in reducing the usually intrusive noise of contra-rotating propellers. “Today, we have demonstrated that we can meet the new noise standards,” Doussinault said.

A major step in open-rotor development will happen in 2015 in Istres, southeast France, where plans call for testing full-scale propellers. The studies will involve blades made of 3D-woven composites–like those of CFM’s Leap turbofan. “We will start manufacturing the molds early next year,” Doussinault noted.

Aerospace research center Onera also emphasized its role in the effort, including “innovative and even revolutionary approaches,” described by Patrick Wagner, director of computing, engineering and testing facilities. Onera is now working on a more advanced testbed, dubbed Z49, designed to accommodate an open-rotor model and accompanying fuselage, wing or empennage model. In fact, Onera has already begun the validation phase of Z49 in S1, reportedly using Snecma’s open-rotor model.